EP0025877A1

EP0025877A1 - Ink-jet printing head and ink-jet printer

Info

Publication number: EP0025877A1
Application number: EP80104961A
Authority: EP
Inventors: Francis Chee-Shuen Lee; Ross Neal Mills; Frank Eberhard Talke
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1979-09-24
Filing date: 1980-08-21
Publication date: 1981-04-01
Also published as: JPS5646770A; CA1156706A; US4353078A

Abstract

A drop-on-demand inkjet printing apparatus in which the print head has an ink cavity 22 which is filled with ink, and which has a nozzle orifice 26 designed so that ink does not flow out under static conditions. A fluid inlet chamber 28 is provided to receive ink from an ink supply pipe 24 and this chamber 28 is separated from the ink cavity 22 by a narrow gap 32. An electromechanical transducer 36 is mounted on a flexible plate 34 overlying the gap 32 between the ink cavity 22 and the inlet chamber 28. The transducer is selectively energized in response to the print data signals so that, when energized by an electrical signal, the transducer flexes the plate 34 to reduce the volume in the ink cavity 22 to eject one ink drop 19from the nozzle orifice 26 and substantiallyto close off the narrow gap 32 to substantially close the back flow path from the ink cavity 22 to the inlet chamber 28 during the formation of the drop of ink.

Description

The invention relates to ink jet printing heads and is more particularly concerned with ink jet printing heads for generating ink drop on demand under control of suitable electrical signals.
Some known ink jet printing systems use a pressure generated continuous stream of ink, which is broken into individual drops by a continuously energized transducer. The individual drops are selectively charged and deflected either to the print medium for printing or to a sump where the drops are collected and recirculated. Examples of these pressurized systems include U.S. patents Nos. 3,596,275 and 3,373,437. Other known ink jet printing systems use a transducer to generate ink drops on demand. One example of such a system is disclosed in U.S. patent 3,787,884. In this system the ink is supplied to a cavity by gravity flow and a transducer mounted in the back of the cavity produces motion when energized by an appropriate voltage pulse, which results in . the generation of an ink drop. A different embodiment of a drop-on-demand system in which the transducer is radially arranged is shown in U.S. patent 3,683,212 to Zoltan.
_U.S. patent No. 3,852,773 discloses an ink jet head in which ink is supplied to a nozzle chamber through an ink feed passage from an inlet chamber to which ink is supplied under gravity from an ink source. Flow between the ink source and the inlet chamber is controlled by an automatic valve arrangement which is rendered operative by surges in the ink caused by movement of the head along the line of printing. Droplet forming pressure perturbations are established in the nozzle chamber by A.C. energisation of a transducer but these perturbations do not cause operation of the valve arrangement and ink flow between the inlet and nozzle chambers in both directions is not restricted by energisation of the transducer.
At page 909 of the IBM Technical Disclosure Bulletin Vol. 15, No. 3, August 1972, there is dislcosed a high-speed droplet generator in which droplets are formed in synchronism with the A.C. energisation of a piezoelectric transducer. The transducer causes vibration of a diaphragm forming one wall of a nozzle chamber which communicates with an outlet nozzle. Ink is supplied to the nozzle chamber through a supply channel or groove formed in a plane surface of a cover or nozzle plate abutting the diaphragm. However, vibration of the diaphragm does not restrict flow of ink along the channel or groove into or back from the nozzle chamber.
The prior art drop-on-demand printing systems have been limited by low drop production rate, by a low efficiency and by a jet instability which produced drops with irregular spacing and/or size which lead to poor print quality as the drop rate was increased. One reason for the low drop production rate in prior art drop-on-demand printing systems is the time required to replenish the ink after ejection of a drop, and a second reason is that, to prevent unwanted ink drop satellite formation, complete damping of the internal fluid oscillations within the ink must be attained before drop ejection can be repeated. A basic reason for the low efficiency of prior art drop-on-demand printing systems is that, during the operational cycle of a drop-on-demand print head, ink is moved not only in the downstream direction toward the nozzle, but also in the upstream direction toward the ink supply. If the impedance in the upstream supply line is much smaller than that in the nozzle, most of the kinetic energy generated in the head is used to accelerate the ink toward the ink supply and only a small fraction of the generated kinetic energy is used to eject droplets out of the nozzle. If the impedance of the upstream supply line is made much higher than that of the nozzle, then ink cannot be resupplied fast enough to the ink cavity, and the drop-on-demand print head will not operate properly. To avoid either of the limiting cases, the impedance of the upstream and downstream fluid line has been generally chosen to be of the same order of magnitude. This implies that the efficiency of the prior art drop-on-demand print heads is substantially below optimum efficiency.
It is therefore the object of this invention to produce an improved drop-on-demand printing system having a higher production rate of ink drops having uniform size and spacing.
It is another object of this invention to produce an improved drop-on-demand printing system in which the impedance of the upstream supply line is varied dynamically during a drop ejection cycle.
These and other objects are attained by an ink jet printing apparatus, for example a drop-on-demand ink jet printer, which comprises a print head having an ink chamber supplied with liquid ink. A nozzle orifice is in communication with the ink chamber and a relatively narrow passageway joins the ink chamber to an ink inlet chamber. An electromechanical transducer is mounted adjacent to the two chambers. Selective operation of the printing apparatus is provided by energizing the transducer in response to an electrical signal, such energisation causing the transducer to reduce the volume in the ink chamber and substantially to close the narrow passageway thereby to force a single drop of ink from the orifice and substantially to prevent ink flow back from the ink chamber to the ink inlet chamber during formation of the drop of ink.
Accordingly, the invention provides an ink jet printer head comprising a nozzle cavity to contain ink in which pressure perturbations are established to cause individual ink droplets, one for each perturbation, to be ejected from a nozzle communicating with the nozzle chamber and a passageway through which ink is supplied to the nozzle chamber, characterised by the provision of an arrangement for limiting or preventing backward flow of ink along the passageway during establishment of the pressure perturbations.
The invention also provides an ink jet printing head comprising a nozzle chamber communicating with an outlet nozzle and, via an ink feed passage, with an inlet chamber to which ink is supplied from an ink source, and electro-mechanical transducer means operable when energised by a suitable electric pulse, to establish a pressure perturbation in the ink in the nozzle chamber capable of causing ejection of an ink droplet from the nozzle, characterised in that the transducer means are operable at least partially to close the ink feed passage so as to restrict back flow of ink therethrough from the nozzle chamber to the inlet chamber due to the pressure perturbation.
Conveniently the transducer means comprise a flexible element forming a wall of the nozzle chamber and flexing during energisation of the transducer means to vary the volume of the nozzle chamber and to reduce the flow cross-sectional area of the ink supply passage.
The invention also provides a drop-on-demand ink jet printing head comprising a nozzle chamber for receiving ink; an inlet chamber separated from said nozzle chamber by a relatively narrow passageway; a nozzle orifice communicating with said nozzle chamber; electromechanical transducer means mounted adjacent said inlet chamber and said nozzle chamber; said transducer means being selectively actuable in response to electrical signals to provide deflection of a deformable element to reduce the volume of said nozzle chamber and substantially to close said relatively narrow passageway to force a single drop of ink from said orifice and substantially to prevent the flow of ink back from said nozzle chamber to said inlet chamber during formation of the drop of ink.
The invention will now be further described with reference to the accompanying drawings, in which:-

FIG. 1 is a plan view of part of a drop-on-demand ink jet printer embodying the invention.
FIG. 2 is a section view taken along line 2-2 of Figure 1.
Fig. 3 is a view, partially in section, of part of another drop-on-demand ink jet printer embodying the invention.
_FIG. 4 is a section view taken along lines 4-4 in Figure 3.
FIG. 5 is a view, partially in section, of part of a further drop-on-demand ink jet printer emboyding the invention.
FIG. 6 is a diagram showing the voltage drive pulses for operating a printer embodying the present invention.

Referring to Figure 1, the printer comprises a print head 10 to which is supplied liquid ink from ink supply means 12. Control means 14 provides the voltage control pulses to selectively energize print head 10 which operates to produce one ink drop for each voltage pulse supplied to print head 10. Print head 10 comprises head body 20 having a nozzle chamber or cavity 22 formed therein. Cavity 22 is maintained filled with ink through supply line 24 from ink supply means 12. Ink from supply means 12 is not pressurized so the ink in cavity 22 is maintained at or near atmospheric pressure under static conditions. An exit from cavity 22 is provided by nozzle portion 26 which is designed so that the ink does not flow out of nozzle portion 26 under static conditions. An intermediate ink reservoir 28 is formed in head body 20 and is separated from cavity 22 by internal wall portion 30. The top of cavity 22 as shown in Figure 1 is closed by a suitable transducer means, which is fixed to the head body. Internal wall portion 30 is designed so that a narrow passageway 32 is provided for the transfer of liquid ink from intermediate ink reservoir 28 to ink cavity 22. The transducer means comprises a membrane member 34 which is fastened to an electromechanical transducer 36. Transducer 36 contracts radially when energized with a suitable voltage pulse and bends membrane 34 inwardly (as shown dotted in Figure 2), and decreases the volume of cavity 22 so that liquid ink is expelled out through nozzle portion 26 to form a single drop. Control means 14 provides the voltage control pulses to selectively energize transducer 36 to produce one ink drop for each voltage pulse applied to transducer 36.
As shown in Figure 6, the voltage pulses to selectively energize transducer 36 are formed at equal intervals T so that a maximum drop production rate is established by the repetition frequency (equal to 1/T) of the voltage pulses. The magnitude of the voltage pulses is V , D and this magnitude is substantially lower than that required in prior art drop-on-demand print heads. For example, voltage pulse 16 produces ink drop 17 and the next voltage pulse 18 produces ink drop 19. The spacing between ink drops 17 and 19 should be constant to produce printed data with acceptable print quality. If it is desired to produce a drop during the next interval T, a voltage pulse (shown dotted in Figure 6) will be produced to produce a subsequent drop spaced a distance Xgfrom drop 19. In the event that the data to be printed requires no drop at that position, then no pulse will be produced. To maintain good print quality, it is required that the missing drop or drops have neglible effect on any other drops produced, either prior to or subsequent to the missing drop or drops.
The above described structure operates in a novel manner to dynamically vary the impedance of the upstream supply line during the operation of the print head. When the transducer 36 is energized, membrane 34 bends downward as shown dotted in Figure 2, decreases the small gap defined by narrow passageway 32, and effectively seals intermediate reservoir 28 from the ink cavity 22. It is not necessary that narrow passageway 32 be completely physically sealed off, since the pressure at that point is changing in proportion to the rate of change of speed or velocity of membrane 34. Since this velocity is changing at a high rate, the gap is effectively sealed off even though it is not physically sealed off. The motion of membrane 34 in Figure 2 is exaggerated for illustrative purposes, but the actual motion is much less as will be apparent to those skilled in the art. It is apparent that in the "sealed off" position, fluid is ejected only in the forward direction when membrane 34 deflects further. When membrane 34 relaxes, the gap defined by narrow passageway 32 between membrane 34 and internal wall portion 30, opens again and the ink is sucked in from the intermediate reservoir 28 to ink cavity 22. In this phase, the gap defined by narrow passageway 32 serves as an upstream/downstream fluid isolator by means of a viscous damping of any disturbance, but allows fluid to enter cavity 22 with relatively low fluid impedance. Experience has shown that the driving voltage requirement for the dynamic impedance matching head is reduced from that of conventional heads due to its greater efficiency. Furthermore, an extremely stable jet is observed due to reduced wave interactions, decreased upstream influence and increased damping between the ink supply 12 and ink cavity 22. Experience has also shown that the print head can produce drops of constant size and uniform spacing at a much greater asynchronous drop rate than has been possible with prior art print head designs.
A planar version of the dynamic impedance matching print head design is shown in Figure 3. In this embodiment, an elongated ink cavity 42 is provided in head body 40. Ink cavity 42 is separated from an intermediate cavity 44 by a cross wall portion 46 that is slightly lower than the surrounding material. Thus, a narrow passageway 48 is formed between cross wall portion 46 and the transducer means 49. Transducer means 49 comprises membrane 50 and electromechanical transducer 52 fixed to the head body 40, so that passageway 48 is formed when the membrane is in a relaxed state, as shown in full line in Figure 4. Conversely, the gap formed by narrow passageway 48 is decreased and substantially sealed off during the deflection of membrane 50 to produce ink drop 56. Since the fluid impedance in the direction toward the ink supply 12 is increased during the downward motion of membrane 50 and decreased during its relaxation, a dynamic variation of the supply line impedance results with a consequent increase in the performance of the print head in producing ink drops from a drop-on-demand print head.
Another embodiment of the print head which applies the dynamic impedance matching technique to a print head utilizing a radially arranged transducer means is shown in Figure 5. The print head comprises cylindrical transducer member 60 closed at one end by a nozzle plate 62, having formed therein nozzle portion 64. The other end of the transducer is fixed to body member 66 and intermediate the ends of transducer 60 is a concentrically mounted plug member 68. Plug member 68 is designed so that a narrow passageway 70 is formed between the outer peripheral surface of plug member 68 and the inner face of transducer member 60. Plug member 68 is supported by rod member 72 from support means 74, which is fixed to body member 66. Support means-74 is provided with sufficient openings so that ink freely flows from ink supply means 12 and supply line 24 to intermediate cavity 76. When transducer 60 is actuated by a suitable voltage drive pulse, transducer 60 is deflected to the position shown dotted in Figure 5 to substantially close off passageway 70 between intermediate cavity 76 and ink cavity 58. Contraction of the volume in ink cavity 58 by energization of transducer 60 causes a single drop of ink 78 to be expelled out through nozzle portion 64. Relaxation of transducer 60 then re-opens passageway 70 to permit ink to flow from intermediate cavity 76 into ink cavity 58.
Thus, it can be seen that time dependent impedance variations in the upstream supply line increases the efficiency and the damping characteristics of drop-on-demand ink jet nozzle designs by closing the supply line during the ejection cycle and opening the supply line to a controlled gap during the refill part of the operational cycle. Embodiments of this design have been described and experience with these embodiments have shown that reduced driving voltages are required due to the increased efficiency. In addition, substantial increases in the drop production rate and increased drop stability have been observed, using the print head with the dynamic impedance adjustment feature as discussed above.
The specific design of the print head can vary widely, based on a number of design considerations and characteristics of the ink being used as known in the art. A specific design built in accordance with the embodiment shown in Figure 1 had a narrow passageway 32 about 25 micrometers high and a width of internal wall portion 30 of about 250 micrometers. The nozzle diameter was about 50 micrometers. This print head produced a drop rate in binary drop-on-demand operation, i.e., asynchronous operation, which is increased by a factor of more than three above the corresponding drop production frequency achievable with otherwise similar print head designs, but without dynamic impedance matching.

Claims

1. An ink jet printer head comprising a nozzle cavity to contain ink in which pressure perturbations are established to cause individual ink droplets, one for each perturbation, to be ejected from a nozzle communicating with the nozzle chamber and a passageway through which ink is supplied to the nozzle chamber, characterised by the provision of an arrangement for limiting or preventing backward flow of ink along the passageway during establishment of the pressure perturbations.

2. An ink jet printing head comprising a nozzle chamber (22, 44, 58) communicating with an outlet nozzle (26, 43, 64) and, via an ink feed passage (32, 48, 70), with an inlet chamber (28, 42, 76) to which ink is supplied from an ink source 12, and electro-mechanical transducer means (36, 52, 60) operable when energised by a suitable electric pulse, to establish a pressure perturbation in the ink in the nozzle chamber capable of causing ejection of an ink droplets (19) from the nozzle, characterised in that the transducer means (36, 52, 60) are operable at least partially to close the ink feed passage (32, 48, 70) so as to restrict back flow of ink therethrough from the nozzle chamber (22, 42, 58) to the inlet chamber due to the pressure perturbations.

3. An ink jet printing head as claimed in claim 2, further characterised in that the transducer means comprise a flexible element (34, 50, 60) forming a wall of the nozzle chamber and flexing during energisation of the transducer means to vary the volume of the nozzle chamber and to reduce the flow cross-sectional area of the ink supply passage.

4. An ink jet printing head as claimed in claim 3, further characterised in that the nozzle chamber is separated from the inlet chamber by a weir-wall (30, 46, 68) having a surface opposed to but spaced away from the flexible element so that a gap is formed therebetween, which gap is closed or at least reduced in extent during flexing of the flexible element.

5. An ink jet printing head as claimed in claim 4, further characterised in that the inlet chamber is formed as an annular chamber surrounding the nozzle chamber and separated therefrom by an annular weir-wall.

6. An ink jet printing head as claimed in claim 4 or 5, further characterised in that the gap between the surface of the wall and the flexible element in its unflexed position is about 25 micrometers.

7. A drop-on-demand ink jet printing head comprising a nozzle chamber (22, 44, 58) for receiving ink; an inlet chamber (28, 42,-46) separated from said nozzle chamber by a relatively narrow passageway (32, 48, 70); a nozzle orifice (26, 43, 64) communicating with said nozzle chamber; electromechanical transducer means (36, 52, 60) mounted adjacent said inlet chamber and said nozzle chamber; said transducer means being selectively actuable in response to electrical signals to provide deflection of a deformable element (34, 50, 60) to reduce the volume of said nozzle chamber and substantially to close said relatively narrow passageway to force a single drop of ink from said orifice and substantially to prevent the flow of ink back from said nozzle chamber to said inlet chamber during formation of the drop of ink.

8. An ink jet printer comprising a printing head as claimed in anyone of claims 1 to 6.